If you maintain a podcast, music server, or any audio pipeline that needs consistent volume across files, there's a non-trivial chance you have one of these somewhere: RUN apt-get install -y mp3gain Or in a beets config: replaygain: backend: command command: mp3gain Or buried in a cron job from 2014. mp3gain was written in C by Glen Sawyer in 2003. Upstream development stopped around 2009. D